| Perhaps the most clandestine, yet vital and widely conserved sensory modality utilized by vertebrates is their balance and sense of orientation in space. The inconspicuous vestibular system is often paired with the auditory system in research due to their anatomical proximity in the inner ear, shared susceptibility to ototoxic substances, similarity in sensory cell structure, and mutual degradation with age. However, vestibular disorders affect 69 million Americans and costs associated with vestibular disorder treatment exceed 20 billion dollars a year in the US. Damage or degradation to the hair cells responsible for vestibular and auditory function is believed to be irreversible in humans. However, amphibians maintain the ability to regenerate hair cells post-embryonically and after injury. Research characterizing the structures and molecular mechanisms responsible for continued vestibular regeneration in anamniotes through adulthood is lacking. This study lays the foundation for future vestibular regenerative work by characterizing the ultrastructure and creating a transcriptomic profile of the semicircular canals of the amphibian model X. laevis. The cellular and synaptic architecture of the X. laevis cristae ampullares were analyzed using TEM and confocal microscopy. Fluorescent images show innervations from the VIII cranial nerve to the hair cells of vestibular canals and the overall structure of the endorgran sensory field using labels for acetylated alpha tubulin and F-actin. TEM images and serial sections reveal regional differences in distribution of the type, innervation, and density of hair cells. Peripheral regions of anterior and horizontal cristae show greater hair cell density, larger ribbon bodies, and a greater proportion of club-shaped hair cells; where as, lower hair cell density, smaller ribbons, and a predominance of cigar shaped hair cells identify central regions. Complementary analysis of the transcripts associated with the vestibular structures found 11 differentially expressed probe set identifiers (Xl-PSIDs). Filters for intensity value and a fold change minimums reduced the number of differentially expressed Xl-PSIDs to 4. Understanding the cellular and synaptic architecture of a vestibular system capable of regeneration lays the foundation for the development of biomedical treatments for millions of people who are affected by vestibular dysfunction. |
